The present invention relates to the field of broadcasting digital services to terminals retrieving these services. More particularly, the present invention is concerned with the problem of the reliability of the broadcasting chain.
Networks broadcasting digital services are becoming widespread. Mention may be made for example of the terrestrial digital video broadcasting standard DVB-T (“Digital Video Broadcasting—Terrestrial”): “ETSI EN 300 744 V1.5.1, Digital Video Broadcasting (DVB): Framing Structure, Channel Coding and Modulation for Digital Terrestrial Television”, and the digital video broadcasting standard for mobile terminals DVB-H (“Digital Video Broadcasting—Handheld): “ETSI EN 302 304, DVB-H—Transmission System for Handheld Terminals”. 
In such broadcasting networks, the services are individually encoded by a set of encoders. Each of these encoders has contents forming the service for which it is responsible. Such contents can comprise video sequences, audio sequences, texts or even interactive applications. On output of each encoder, each service is available in the form of a digital data stream comprising a set of packets. These services are then multiplexed by a multiplexer. This operation consists of constructing a stream that mixes the data packets of the various services before being broadcast. This results in a digital data stream comprising the data of the different services. Use may be made of the transport stream format MPEG-2 TS (Moving Picture Experts Group-2 Transport Stream) described in the document “ISO/CEI 13818-1, Generic Coding of Moving Pictures and Associated Audio Information: Systems” or the format according to the Internet Protocol IP.
In the context of a microwave radio transmission, the stream is intended to be sent in the form of a radio signal by one or more modulators. To do this, the stream has to be shaped by a formatting module. This formatting may, for example, consist of inserting synchronization labels in the stream, in such a way as to allow the modulator or modulators to synchronize the transmission of the radio signal in the context of a distribution of the SFN (“Single Frequency Network”) type.
The patent document WO 2009/112371 A1 describes a broadcasting system having a duplicated formatting module. This broadcasting system allows a modulator to switch between the two streams generated by the two formatting modules without becoming desynchronized. These formatting modules are synchronized with each other in order to generate synchronized streams. A modulator can thus switch from a first stream generated by one of the formatting modules to a second stream generated by the other formatting module, without need for resynchronizing the modulator. In this way, an incident occurring in the generation of the stream does not automatically result in a service interruption.
However, the broadcasting system described in this document WO 2009/112371 A1 is not suitable for an implementation in the context of a broadcasting based upon the second-generation digital terrestrial video broadcasting standard DVB-T2: “EN 302 755 V1.1.1, Frame Structure, Channel Coding and Modulation for a Second Generation Digital Terrestrial Television Broadcasting System”. Indeed, the synchronization performed between MPEG2 TS transport streams does not prevent from resynchronization at the level of the modulator in this context.
The same problem occurs in the context of other digital service broadcasting chains, if they show redundancy through the use of a plurality of digital service streams representing the same digital service, these streams being encapsulated in respective transport streams.
It is desirable to overcome these various drawbacks of the prior art.